[GHC] #8936: Irrefutable pattern failed in ghc 7.4.1

[GHC]

#8936: Irrefutable pattern failed in ghc 7.4.1
----------------------------------+---------------------------------
       Reporter:  gahuber95       |             Owner:
           Type:  bug             |            Status:  new
       Priority:  normal          |         Milestone:
      Component:  GHCi            |           Version:  7.4.1
       Keywords:                  |  Operating System:  Linux
   Architecture:  x86_64 (amd64)  |   Type of failure:  None/Unknown
     Difficulty:  Unknown         |         Test Case:
     Blocked By:                  |          Blocking:
Related Tickets:                  |
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 Thanks for your attention!  Gary (newbie)

 ##########################################
 class Show a => Show_Listable a where
   show_list ::  [a] -> IO()


 instance Show_Listable a -> Show a where
   show_list lst = do
     print "gen list";
     print lst

 lst :: Int -> [Int]
 lst i = [1,2,3]

 main = do
     show_list (lst 1)

 ######################################################
 Output:

 $ ghc bull.hs -o bull
 [1 of 1] Compiling Main             ( bull.hs, bull.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.4.1 for x86_64-unknown-linux):
         compiler/rename/RnSource.lhs:429:14-81: Irrefutable pattern failed
 for pattern Data.Maybe.Just (inst_tyvars,
                                                         _,
                                                         SrcLoc.L _ cls,
                                                         _)


 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8936>
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